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https://issues.apache.org/jira/browse/MAPREDUCE-6541?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14994678#comment-14994678
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Wangda Tan commented on MAPREDUCE-6541:
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[~Naganarasimha], that's also different: MAPREDUCE-6514 is to fix bug in
existing reducer preemption logic (remove reducer request locally but not
notify RM). This is an enhancement of how to calculate available mapper slots.
> Exclude pending reducer memory when calculating available mapper slots from
> headroom to avoid deadlock
> -------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-6541
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6541
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Wangda Tan
>
> We saw a MR deadlock recently:
> - When NM restarted by framework without enable recovery, containers running
> on these nodes will be identified as "ABORTED", and MR AM will try to
> reschedule "ABORTED" mapper containers.
> - Since such lost mappers are "ABORTED" container, MR AM gives normal mapper
> priority (priority=20) to such mapper requests. If there's any pending
> reducer (priority=10) at the same time, mapper requests need to wait for
> reducer requests satisfied.
> - In our test, one mapper needs 700+ MB, reducer needs 1000+ MB, and RM
> available resource = mapper-request = (700+ MB), only one job was running in
> the system so scheduler cannot allocate more reducer containers AND MR-AM
> thinks there're enough headroom for mapper so reducer containers will not be
> preempted.
> MAPREDUCE-6302 can solve most of the problems, but in the other hand, I think
> we may need to exclude pending reducers resource when calculating
> #available-mapper-slots from headroom. Which we can avoid excessive reducer
> preemption.
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